A conventional semiconductor laser of a stem type, which is applied to a CD-use pick-up or the like and capable of preventing astigmatism, has a structure shown in FIG. 6. In this example, a metal material such as iron is formed by a cold forging method so that one portion in the center of a base 21 is raised to form a heat sink portion 22, and leads 23 and 25 are secured thereto using glass 26 or the like to form a stem 20, and in this stem 20, a laser chip 31 is mounted on the heat sink unit 22 through a sub-mount 34 made of a silicon substrate or the like, and one of electrodes (on the rear side of the chip 31) is electrically connected to the lead 23 by a wire 33 through a relay portion 38 of the sub-mount 34, with the other electrode being connected to the sub-mount 34 through a wire 33; thus, the other electrode is electrically connected to a common lead 24 via the heat sink portion 22 and the base 21 through the rear face of the sub-mount 34.
Here, reference numeral 32 represents a monitor-use light-receiving element in which one of electrodes is electrically connected to the lead 25 through the wire 33, with the other electrode being electrically connected to the common lead 24 through the sub-mount 34, the heat sink unit 22 and the base 21. Further, a cap 35 is put on the periphery thereof, and a through hole 35a is formed in the center of the top of the cap 35 so as to allow light emitted by the laser chip 31 to penetrate, and a glass plate 36 is sealded thereto by using a bonding agent (low melting-point glass) 37 so as to seal the through hole 35a. As shown in FIG. 6, the top of the cap 35 is cut diagonally, and the glass plate 36 having a predetermined thickness is placed so as to tilt with not 90°, but a predetermined angle to the direction of the laser beam in the lamination in-plane (x-y plane) of the semiconductor layer of the laser chip 31 so that an astigmatic difference with the opposite sign, which has the same amount as the astigmatic difference generated in the laser chip 31, is generated to correct the astigmatism; and this method has been proposed (for example, by Japanese Examined Patent Publication No. Hei 5-6261 (FIG. 2)).
As shown in FIG. 7, for example, Japanese Laid-Open Patent Publication No. 2001-284695 has proposed a structure of a semiconductor laser to be used in an optical disk system such as CDs, in which a package 42 is formed by a lower mold 42a and an upper mold 42b by using a lead frame 41 with an optical isolator 43 being installed on its light-outgoing face. In FIG. 7, reference numeral 44 represents a sub-mount, 45 represents a laser chip and 46 represents an opening section of a resin mold.
As described above, with respect to the conventional semiconductor laser for use in a pickup of a CD, DVD or the like, a package having the can-type structure has been mainly used, and in order to correct the astigmatism on the semiconductor laser side, the package needs to be molded into a special shape with the cap being diagonally cut. In order to correct astigmatism, such a can-type structure requires an expensive cold-forging stem and also needs to form a special shape with the cylinder-shaped cap being diagonally cut, and this structure raises a problem of high costs. In particular, in order to correct the astigmatism, the angle to the outgoing direction of a laser beam and the thickness of a transparent plate needs to be strictly determined in accordance with the astigmatic difference of the laser beam that is emitted by the laser chip; therefore, not only the forming process of the cap, but also factors such as rotation at the time of welding the cap need to be strictly controlled, and these also cause high costs. Moreover, because of increase of a number of parts required, the can-type structure needs to prepare a number of processes and a difficult engineering technique, resulting in degradation in the yield.
In the case of a so-called frame-laser structure using a lead frame, as shown in FIG. 7, a structure in which an optical isolator is bonded to the end face of a mold resin has been proposed. However, in the case of a structure in which a transparent plate or a circular polarizing plate (optical isolator) is simply placed, even when the end face of resin is not a flat face and is slightly tilted, the resulting adverse effects are small; in contrast, in the case of a structure that requires a strict layout of a transparent plate in which, in order to correct the astigmatism, the transparent plate having a predetermined thickness needs to be placed at right angles to the semiconductor lamination plane of the laser chip with a tilt at a predetermined angle from 90° with respect to the axis direction of the laser beam, in a molded resin formed by an upper mold and a molded resin formed by a lower mold, the end faces of the molded resins are not made coincident with each other, resulting in a step difference between the upper mold and the lower mold on a parting line and the subsequent tilt in a circular polarizing plate or the like to be bonded to the end faces; therefore, this structure that the transparent plate is bonded in a manner so as to bridge the upper mold resin and the lower mold resin, rises a problem that fails to provide desired properties.